Connection Components In Profibus; Rules For The Laying Of Profibus Cables - Siemens NCU 7 0.2 Series Manual

Connecting
7.8 PROFIBUS / MPI
Connector features
The bus connector is used to connect the PROFIBUS cables to the PROFIBUS DP
interfaces (X126, X136), thus establishing a connection to additional nodes.
Only bus connectors with a 35° cable outlet should be used in order to ensure that the front
cover can be closed.
7.8.3

Connection components in PROFIBUS

Connection components
Individual nodes are connected by means of bus connectors and PROFIBUS cables.
Remember to provide a bus connector with a programming port at either end of the subnet.
This will give you the option of expanding the subnet if required, for example, for a
programming device.
Use RS 485 repeaters to connect segments or extend cable lengths.
Segments
A segment is a bus line between two terminating resistors. A segment may contain up to 32
nodes. In addition, a segment is limited by the permissible cable length, which varies
according to the transmission rate.
Terminating resistor
A cable must be terminated with its own surge impedance to prevent line disturbances
caused by reflections. Activate the terminating resistor at the first and last node on a subnet
or segment. The control unit must be either the first or the last node on the subnet.
Make sure that the stations to which the terminating resistor is connected are always
supplied with voltage during power-up and operation.
7.8.4

Rules for the laying of PROFIBUS cables

Laying of bus cables
During laying of the PROFIBUS cable, you must avoid:
● twisting
● stretching and
● squeezing
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Manual, 02/2011, 6FC5397-0AP20-0BA0
NCU 7x0.2